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Residual-current device
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<p>A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) is an electrical safety device, more specifically a form of <a href="/facts/Earth-leakage_circuit_breaker/40j9stst">Earth-leakage circuit breaker</a>, that interrupts an <a href="/facts/Electrical_Circuit/zt94kTW0">electrical circuit</a> when the current passing through line and neutral conductors of a circuit is not equal (the term <i>residual</i> relating to the <a href="/facts/Remainder/wCmbYeeh">imbalance</a>), therefore indicating <a href="/facts/Leakage_(electronics)/Nd6PNxhV">current leaking</a> to <a href="/facts/Ground_(electricity)/F6TEMIVv">ground</a>, or to an unintended path that bypasses the protective device. The device's purpose is to reduce the severity of injury caused by an <a href="/facts/Electric_shock/LmUdx0Ew">electric shock</a>. This type of circuit interrupter cannot protect a person who touches both circuit conductors at the same time, since it then cannot distinguish normal current from that passing through a person. </p><p>A residual-current circuit breaker with integrated overcurrent protection (RCBO) combines RCD protection with additional <a href="/facts/Overcurrent_protection/gX2g5TNH">overcurrent protection</a> into the same device. </p><p>These devices are designed to quickly interrupt the protected circuit when it detects that the <a href="/facts/Electric_current/Dc1xdnUX">electric current</a> is unbalanced between the supply and return conductors of the circuit. Any difference between the currents in these conductors indicates <a href="/facts/Leakage_current/Nd6PNxhV">leakage current</a>, which presents a shock hazard. Alternating 60 Hz current above 20 <a href="/facts/Ampere/MScqkCgz">mA</a> (0.020 amperes) through the human body is potentially sufficient to cause <a href="/facts/Cardiac_arrest/HIAm9AWX">cardiac arrest</a> or serious harm if it persists for more than a small fraction of a second. RCDs are designed to disconnect the conducting wires ("trip") quickly enough to potentially prevent serious injury to humans, and to prevent damage to electrical devices. </p>